The present invention relates to a reciprocating internal combustion engine including a means of reducing cyclic disturbances for low-speed running.
At the current time, all engine manufacturers are looking to reduce the pollution and consumption of vehicle engines in town.
A first solution consists in stopping the engine at red lights and then re-starting it. This entails coupling a motor-alternator directly to the crankshaft, and this is expensive.
The second solution consists in reducing the rotational speed of the engines at low idle. However, when the low idle speed of an engine is reduced, the cyclic disturbances increase, and this makes its running unstable. The only way to reduce the cyclic disturbances is to increase the moment of inertia of the flywheel. However, this presents numerous drawbacks, namely: it involves a penalizing increase in the mass of the propulsion unit; it necessarily entails improving the performance of the starter motor; and it entails a drop in engine performance, the engine becoming slower to pick up speed.
The arrangement according to the present invention makes it possible to simultaneously obtain two antagonist results, namely: a flywheel with a high moment of inertia for dealing with cyclic disturbances, very greatly reducing these, and a lower moment of inertia for the engine because use is made of a flywheel of lower mass.
In order to achieve this result, use is made of pendular masses associated either with the flywheel or with a pulley on the other end of the crankshaft.
It is known practice for pendular masses to be associated with a crankshaft and one and/or other of its ends in order to damp out the vibrations which arise in the crankshaft itself when subjected to heavy load, which vibrations could cause the crankshaft to break.
In the case of the present invention, these pendular systems are being used not to protect the crankshaft against a risk of breakage due to vibration, but to combat the effects due to the moment of inertia of the engine assembly (crankshaft and pistons) when the engine is running at low speed (that is to say when the crankshaft is subjected to very light load) and is therefore subject to cyclic disturbances.
Such pendular systems are described in U.S. Pat. No. 5,295,411.
Surprisingly, it has been discovered that these same means could advantageously be employed to solve an entirely different problem, namely that of irregularities in the cycle, or xe2x80x9ccyclic disturbancesxe2x80x9d which occur when an engine is running at low speed, the crankshaft then being subject to light load.
When wishing to tackle the problem of vibrations at heavy load, as is the case with the means described in U.S. Pat. No. 5,295,411, there is the desire to tune the pendulum (or pendulums) to the harmonics likely to excite the natural torsional mode of the crankshaft throughout the engine speed range. For a four-cylinder four-stroke engine, this angular frequency is of the order of 30,000 to 40,000 rpm.
By contrast, in the case of the present invention, the pendulum will be tuned to the number of explosions per revolution and this will be done for speeds close to the low idle speed (700 rpm and below), and thus for light load running. In the case of a four-cylinder four-stroke engine, there are two explosions per revolution which means that the pendulums will be tuned to the harmonic 2. The pendulums will therefore be tuned to the harmonic of the cyclic disturbance or, at the very least, to near to the angular frequency of its major harmonic.
This application of these pendular systems, which are known in themselves, to the very specific problem of cyclic disturbances makes it possible to have a moment of inertia adapted to suit rotational speeds of the order of 500 rpmxc2x1200.
These systems, the characteristics of which are calculated to be effective against cyclic disturbances at low speed, are inoperative and without effect at high speed.
According to the invention, at least one element capable, as the flywheel rotates, of having a pendular movement with respect to said flywheel when rotation occurs with cyclic disturbance is coupled to the crankshaft, for example to the flywheel. If xcexa9 is the mean rotational speed of the engine, then it is known that during running, the instantaneous speed varies between xcexa91 and xcexa92; the cyclic irregularity coefficient is       n    =                  "LeftBracketingBar"                              Ω            1                    -                      Ω            2                          "RightBracketingBar"            Ω        ;
it may be calculated that, for a reciprocating internal combustion engine,   n  ≈      k          I      ⁢              xe2x80x83            ⁢              Ω        2            
where k is a constant which represents the amplitude of the variation in engine torque and I is the moment of inertia of the engine-receptor assembly. This shows that cyclic disturbances are at their highest when the mean rotational speed is at its lowest. The use of (a) pendular element(s), suitably tuned, makes it possible to compensate for the cyclic disturbances. The size and mass of the pendular elements, and their positions on the flywheel are advantageously chosen so that they are tuned to the major harmonics of the cyclic disturbances. It is found that, in this way, it is possible to run, for example, a 4-cylinder, 4-stroke engine at average speeds of close to 300 rpm without troublesome irregularities and using a flywheel which is lighter by comparison with those used in the state of the art.
The subject of the present invention is therefore an internal combustion engine, the crankshaft of which is equipped, for example, with a flywheel, characterized in that said flywheel is equipped with at least one pendular element whose size, mass and position on said flywheel are determined so as to be tuned to close to the angular frequency of the major harmonic or harmonics of the cyclic disturbance. For example, for an in-line 4-cylinder 4-stroke reciprocating engine, the major harmonic of the cyclic disturbance has an angular frequency equal to twice the rotational speed.
The present invention may also include the following arrangements taken separately or in combination:
a) the flywheel is equipped with at least two housings in which a flyweight can move freely;
b) the flywheel is equipped with three housings arranged 120xc2x0 apart;
c) the flywheel is equipped with two groups of three housings arranged 120xc2x0 apart, the two groups being interspersed symmetrically and each group having different sizes and positions, and different masses;
d) the side walls of each housing are planar and separated from one another by a runway track, the flyweight being a roller capable of rolling between the side walls along the runway track; as a preference, the roller is a cylinder of revolution;
e) the runway track of the housing, against which the roller rolls, is a surface of revolution about an axis perpendicular to the side walls of the housing;
f) the housing may be a cylinder of revolution;
g) the cross section of the runway track on a plane parallel to the side walls of the housing is a curve determined by calculation according to the desired reaction on the cyclic disturbance phenomena;
h) the side walls of each housing consist of annular cheeks fixed one on each side of the flywheel; the runway track of a housing consists of a ring inserted in an opening made in the flywheel, the interior edge of each annular cheek coming to rest against one end of each ring and constituting a runway track, the means of attaching the flywheel to the crankshaft being arranged in the central region left free by the annular cheeks;
i) the flywheel is equipped with three pendular devices arranged 120xc2x0 apart, each pendular device being double;
j) the flywheel is equipped with two groups of three double pendular devices interspersed symmetrically and having different dimension, position and mass characteristics;
k) the double pendular system consists of a moving mass connected to the flywheel by two axles, each moving both in a housing formed in the mobile mass and in a housing formed in the flywheel;
l) the mobile mass has a T-shaped cross section;
m) the mobile mass has a U-shaped cross section;
n) the monofilar pendular system consists of an asymmetric flyweight borne in pivoting by an axle;
o) the monofilar pendular system consists of a cylindrical flyweight equipped with drillings on just one side, it being possible for these drillings to be separate or combined into a single slot;
p) the monofilar pendular system consists of a sealed casing filled with two immiscible liquids of different densities, for example oil and mercury;
q) the monofilar pendular system consists of a toothed pinion meshing either with a central pinion or with peripheral teeth;
r) the either monofilar or bifilar pendular system is locked in position above a predetermined rotational speed by radial sliders each held by a spring moving under the effect of centrifugal force;
s) the pendular system consists of n flyweights arranged n/360xc2x0 [sic] apart, these flyweights having the shape of a circular sector subtending an angle of n/360xc2x0 [sic] and mounted so that they can pivot on the flywheel;
t) each flyweight in the shape of a circular sector has a bore inside which a mobile mass moves.